In recent years, in public places such as airports and stations, operation information and signage are presented using a video display.
When content is presented in a public place in this way, it is possible to present the content more effectively by using audio in addition to video, but on the other hand, audio will reach an unspecified large number of people who do not need such information.
Therefore, a local sound field forming technique has been proposed, by which the reproduced sound can be heard only in the vicinity of a desired area, and can hardly be heard outside the area.
For example, as a method of forming such a local sound field, a local sound field forming method by means of super-directivity control using a parametric loudspeaker is known.
However, with the method by means of super-directivity control using a parametric loudspeaker, once a parametric loudspeaker is installed, it can only be used for fixed purposes, and some sort of ingenuity is also necessary for safety. Furthermore, since the frequency bands that can be used as reproduced sounds are limited, the reproduced contents are also restricted.
On the other hand, a method of realizing local sound field formation without restricting reproduced contents has also been proposed.
For example, as such a method, a method of generating an evanescent wave by using a loudspeaker array has been proposed (see, for example, Patent Document 1). Furthermore, in order to suppress space truncation errors due to a use of a finite length loudspeaker array for generating an evanescent wave, a method of reducing the errors by performing a windowing in the spatial direction has also been proposed (see, for example, Non-Patent Document 1).
By using the methods described in Patent Document 1 and Non-Patent Document 1, it is possible not only to form a local sound field without limiting reproduced contents, but also to form a local sound field in which leakage of propagating waves in a transverse direction with respect to the loudspeaker array can be suppressed to some extent.